With increasingly demanding good qualities of printing products, spot colors are widely used, in particular, in packaging. When printing by an inkjet printing device, the implementing mechanism of a spot color differs from that of four colors. First, the color matching processes are different, because four-color printing focuses on a general printing effect while spot color printing aims to accurately simulate and reproduce a single spot color. Accurate simulation and spot color output are critical problems to be solved due to the large number and wide range of spot colors. Further, many spot colors are out of the color range of a printer, which causes a great difficulty to the digital printing. Therefore, the current spot color printing is usually performed in a conventional printing manner, which has the problems of time consuming, low efficiency and inaccurate simulation. Even if some digital printing software support the spot color print function, which usually relies on single-point calibration and lacks a good correction mechanism, so it is difficult to accurately reproduce the spot color.
A method for calibrating the spot color based on inkjet printing uses the colors of printing inks contained in the printer instead of a spot color printing ink to simulate a spot color. It will not guarantee the accuracy of simulation. During simulation, a chromatic aberration ΔE of CIE1976 L*a*b color space is used to determine the accuracy of simulation. A bigger value of chromatic aberration means a worse simulation of a spot color. There are many solutions to solve the problem of a large chromatic aberration, such as enlarging the color gamut of the printer, changing the paper, increasing the types of printing inks and so on, but these solutions will add the cost, have limitations in their application and could not function effectively without a good spot color calibration mechanism.